1. Field of the Invention
The present invention relates to crewseats in aircraft such as helicopters, which have adjustable lumbar and thigh supports.
2. Background of the Invention
Support mechanisms for the lumbar spine and thighs are commonly integrated into the structure of crewseats in aircrafts. However, the specific environment of certain aircraft, e.g., helicopters, imposes demanding design requirements. The mechanism must adjust to accommodate a wide range of body types and sizes, it must not affect the aircraft's operation or obstruct egress (i.e., no dangling or bulky components), it must be lightweight, it must be quickly adjustable, it must be relatively inexpensive and maintainable, and it must be highly durable and crashworthy.
Generally, there are three types of supports possible for seating apparatus: inflatable supports, fixed supports and mechanical supports. Inflatable supports comprise one or more inflatable bladders and an inflator. Inflatable supports are often found in automotive seats, but are not suited for use in military aircraft, mainly because bladders cannot maintain a fixed level of support as the differential pressure of the bladders varies with altitude. Additionally, the hand pumps used to inflate the bladders are generally bulb-like appendages that can hinder operation of the aircraft, or block emergency egress. The hand pumps also require an excessive amount of time to inflate and to adjust the bladder size. The inflatable mechanisms require more maintenance than the other mechanisms, and are not as durable.
Fixed support devices generally comprise specially contoured cushions or pads. However, this type of support is poorly suited for use in military helicopters because it offers minimal adjustment capabilities. Occupants having significantly different body sizes and body contours cannot all derive adequate support from such non-adjustable devices. Additionally, these devices are often too bulky for many environments, such as helicopter cockpits.
Mechanical support devices generally provide support to the lumbar spine and thighs using rollers, levers, and camshafts. Adjustable supports for crewseats often rely on a series of link arms and/or threaded screw shafts. Although these types of devices provide satisfactory support in automotive applications, they are not suitable for more demanding environments such as helicopters due to their limited durability under repetitive use and impact loads. For example, U.S. Pat. No. 5,088,790 to Colasanti et al. describes a lumbar support mechanism that uses a screw shaft actuated by a hand crank. When the screw shaft is rotated, a linkage attached to traveling nuts moves a pressure applicator either forward or backward, thus altering the contours of the lumbar region. Similarly, U.S. Pat. No. 4,469,374 to K. Jo et al. uses two threaded axles and moving thread holders. U.S. Pat. No. 5,007,677 to H. Yasuo et al., describes a pivotable lumbar support member whose moving means comprises a link arm, an intermediate link, a drive link and a drive shaft. U.S. Pat. No. 4,465,317 to Schwarz, and U.S. Pat. No. 4,725,095 to Benson, also describe devices with a large number of moving parts.
Unlike these prior art mechanical supports, supports for demanding environments such as helicopters must use a comparatively simple design with a minimum number of moving parts to assure durability and maintainability. For example, helicopters are routinely subjected to vertical impact loads, which can misalign or damage linkages or vertically disposed members.
Another reason why automotive supports cannot be adapted for use in the more demanding aircraft environment is that many automotive mechanisms actuate the lumbar adjustment by shifting the back cushion, or the whole seat back structure up and down. This is particularly unsuited in military aircraft seats that have a solid armor construction. For example, U.S. Pat. No. 4,834,455 describes a seat back that includes a fixed "protruding lumbar support." The seat back, and hence the lumbar support, is adjustable in a vertical direction. Similarly, U.S. Pat. No. 4,531,779 to Hashimoto describes a seat back with a pivotable support mechanism that allows the seat back cushion to "shift upwardly and downwardly as the angular relation of said cushion is adjusted." An additional problem with automotive supports is their relatively poor crashworthiness. Seat backs or cushions that are supported by relatively fragile structural members, such as toothed racks or threaded shafts, do not provide helicopter seats with adequate crash worthiness.
Many of the prior art thigh adjustment devices include rollers, rotatable shafts, or camshafts. Generally, these devices are not suitable for use in helicopters due to the irregular shape of the seat cushion in the helicopter. The rectangular cutout in the front edge of the seat cushion that accommodates the helicopter's cyclic control stick limits the forward travel of moving rollers, or the forward position of camshaft devices, thereby limiting their effectiveness. For example, U.S. Pat. No. 4,324,431 to Heling et al. describes a thigh support design with a slideable thigh support shaft. This invention could only be installed in a helicopter seat if it had a considerably shorter slide path. Another drawback of this invention is that it does not provide significant thigh angle adjustment to accommodate a range of leg lengths.
Another prior art adjustment device for automobiles is disclosed in U.S. Pat. No. 4,491,365 to Murakami. This patent describes a thigh adjustment device with a manually operable lever that converts rotational force of a shaft into vertical lift for adjusting the tilt angle of a "thigh support frame."
These prior art devices are not well suited for crashworthiness. For crash protection purposes, it is desirable to have a minimal amount of distance between the ischial tuberosities and the seat pan. It is also not desirable to have moving parts or linkages disposed directly under the ischial tuberosities. Otherwise, hard landings or survivable crashes may lead to unnecessary personal injury of the crewmember.